1. Field of the Invention
This application relates to the field of high density interconnection systems, and more particularly, to the field of lithography for high density interconnect systems.
2. Prior Art
In high density interconnect systems in which a plurality of integrated circuits are bonded to a substrate and interconnected by placing a dielectric layer over the integrated circuits and the substrate, forming via holes in the dielectric layer and then forming a patterned metallization layer on top of the dielectric layer with the metallization extending into via holes to make contact to the contact pads of the integrated circuits, each metallization pattern must either be individually tailored to the exact positions of the various integrated circuit chips or an adaptive lithography system must adjust an ideal metallization pattern in accordance with the actual position of the various integrated circuit chips. In the above-identified related U.S. Pat. No. 4,835,704, this problem is solved by adaptation of an ideal metallization pattern in accordance with the actual locations of the integrated circuit chips and their pads by modifying the metallization pattern to properly connect to the contact pads. That adaptation is enabled by providing a "picture frame" around the allowed location of each integrated circuit chip in which adaptation of the metal layer takes place. In order to facilitate that adaptation, one of the design rules for the ideal metallization is that each metal path which crosses the picture frame must do so perpendicular to those edges of the picture frame which it crosses. The ideal metallization pattern over the chip is maintained with respect to the chip and thus, must be shifted and/or rotated with respect to the portion outside the picture frame in accordance with any shift and/or rotation of the chip with respect to its ideal location. The ideal metallization pattern beyond the outer edge of the picture frame is maintained with respect to the substrate, i.e. unchanged during the adaption process. Adaption to the actual chip location is accomplished by modifying the metallization pattern within the picture frame area to properly connect from the ideal metallization pattern at the outside edge of the picture frame to the shifted/rotated ideal metallization pattern over the chip. This results in the angling of conductors in the picture frame area where the chip is displaced perpendicular to or rotated with respect to the ideal direction of those connections.
I have found in adapting the "Omnicards" hybrid circuit layout program available from Task Technologies, Inc. of Rochester, N.Y., to handle the original routing of the metal conductors in the ideal metallization pattern that the requirement that all wires cross the picture frame perpendicular to the edges thereof substantially complicates the routing problem for the software, and in many cases, results in a failure to connect all nodes as is required.
It is known in the integrated circuit art to open a via hole over the center of a contact pad and to provide a contact frame (an enlarged portion of the conductive run) in the pattern of the overlying metal in order to compensate for potential misalignments between the mask which defines that overlying metal and the underlying metal to be contacted.
An alternative adaptive lithography technique which is more compatible with hybrid circuit layout programs is needed.